1. Field of the Invention
The presents invention relates to a device and a method for influencing the vibration of a planar element having two opposite surfaces and a neutral fiber plane running between the two surfaces, at least one actuator and at least one sensor, which each are provided with transducer materials and are connected to an electronic component or an electronic module. Preferably a printed circuit board can be used as the planar element.
2. Description of the Prior Art
Devices for influencing mechanically vibrating planar elements are employed in numerous technical fields, for example in acoustics, in the automobile industry and in the air and space industry.
The increasing interconnection of classical mechanical engineering and information technology, especially in the disciplines of mechatronics and adaptronics, is leading to an increasing use of electronic modules on printed circuit boards, for example in the fields of automobile manufacturing, in the air and space industry but also in machine tool manufacturing. Excitation of resonance in the circuit board leads to elastic deformations which can result in considerable elongation and buckling along the surface of the printed circuit board, thereby burdening the strip conductors on the surface and the applied electronic components. Tearing or damaging of the conductor strips can lead to damaging the printed circuit board itself, soldering and other connections may fail. Applied components may be damaged by the mechanical tensions or lead to failure of the electronic module. Consequently, there is a need for dampening such type vibrations in the electronic modules.
State of the art are passive devices for influencing vibration of planar elements, for example by means of a special construction design, such as mechanical stiffening in the form of bracing or by using vibration-dampening materials in the respective planar elements. Apart form this, there are state-of-the-art devices which result in mechanical decoupling the vibrations of planar elements from their surroundings, for example by using suited holding means.
Due to their efficiency, such type passive devices for influencing vibration find wide use for dampening undesired mechanical vibrations. A drawback is, however, the required additional space and additional weight. Moreover, the efficacy of influencing vibration is dependent on the to-be-influenced vibration frequency. In general, efficacy decreases distinctly at low frequencies, consequently it is impossible to employ passive systems for applications below frequencies of a few hundred Hz.
State-of-the-art alternative methods for influencing the vibration of planar elements use active systems usually having at least one sensor and one actuator which are connected to a control unit, and the sensor and the actuator are actively connected to the planar element. In general, the mentioned components form a control circuit which permits controlling the actuator in a defined manner based on the signals detected by the sensor. The sensor detects directly or indirectly the amplitude, the frequency and the phase position of the vibrations of the planar elements. Should, for example, the present vibrations of a planar element be dampened, control signals having a certain phase position, frequency and amplitude relative to the sensor signal are conveyed to the actuator by means of which counter vibrations are induced in the planar element that compensate the vibrations of the planar element. The actuator can also be utilized to excite and reinforce defined vibrations of a planar surface or to introduce defined shear, pressure or tensile forces on the planar element.
Piezoelectric transducers have proven to be particularly well suited as actuators for influencing the vibration in thin planar elements. Thus such type actuators having various piezoelectric materials in various shapes and sizes particularly in the form of planar piezoelectric transducers are used. Employed as sensors are various components such as acceleration recorders, wire strain gauges or piezoelectric transducers as well. The advantage of using transducer materials for influencing the vibration of planar elements is, among other things, the low weight and small size as well as being able to use them at vibration frequencies from several Hertz to a few kilohertz.
U.S. Pat. No. 4,565,940 describes a generic device in which an actuator is used which is an organic polymer with piezoelectric properties. Such types of polymers, such as for example polyvinylidenefluoride (PVF2) are usually made in the form of foils. In the described device, a PVF2 foil is placed on a surface of a planar element acting as a piezoelectric actuator. Used as sensors are acceleration meters or wire strain gauges which are also placed on the surface of the planar element. With the piezoelectric foil actuator placed on only one side of the planar element not only bending moments but also longitudinal forces are conveyed into the planar element. As the two effects overlap, the efficacy of the active influencing of vibration, however, is unfavorably influenced.
In order to solve this problem, EP 0 806 589 proposes, apart from applying a piezoelectric actuator on the surface of a planar element, attaching an acceleration sensor which records the vibrations and which is attached to the free surface of the actuator. The actuator and the sensor attached to it are placed on the surface of the planar element in such a manner that the actuator and the sensor are placed basically in the maximum vibration bulge formed with resonant excitation of the planar element. This device however has the drawback that due to the arrangement of the actuator and the sensor attached to it, parts of the surface of the planar element are no longer available for other uses.
Moreover, EP 0 975 981 describes a printed circuit board arrangement with active vibration dampening in which the actuators are placed on supporting elements in order to have as much area as possible of the printed circuit board available for the actual electronics. Being placed on supporting elements, however, renders the actuators susceptible to damage. Furthermore, it makes selective introduction of actuator forces into the planar elements more difficult.
All active devices for influencing vibration of a planar element require power electronics to trigger the actuator and/or the sensors.
The prior art devices and methods for influencing vibration of a planar element, in particular for a printed circuit board, in which actuators and/or sensors are used have the following disadvantages:                The actuators and sensors are directly or indirectly attached on the surface of the planar element, covering it at least partly. The area required for this is lost for other uses, for example for further electronic components. Moreover, the actuators and sensors disposed on the surface are exposed making them susceptible to damage from external influences, in particular if the actuators or sensors are placed on supporting elements.        By placing the actuators and sensors on only one side of the surface of the planar element, not only bending moments but also longitudinal forces are introduced respectively recorded. The overlapping of the two effects impairs the efficacy of active influencing of vibration.        The actuators and/or sensors are used inside an electrical control circuit. Triggering the actuators and/or sensors requires power electronics, consuming additional electric energy.        